Field
Embodiments of the present invention relate to a laser welding head.
Related Art
When repair work is performed in a nuclear reactor, there is a place such as a narrow place which is difficult to access in the nuclear reactor. In order to increase the accessibility, a laser welding apparatus, which has small heat input and which can be made small in size, has been developed. As for a laser welding head for laser welding work to repair a nuclear reactor, various configurations have been proposed to reduce damage of the laser welding head, the damage being caused by the reflected light from a base material and the radiant heat from the molten pool.
As configurations adopted to reduce thermal damage of the laser welding head, there are proposed an underwater welding apparatus, an overlay welding apparatus, an overlay welding method for a reactor internal structure in a nuclear reactor, and the like. The proposed underwater welding apparatus includes the laser welding head configured by an aluminum alloy or a copper alloy having high thermal conductivity and therefore improves mechanical and thermal durability.
Further, in the proposed overlay welding apparatus, when the flow rate of the shielding gas is set to 6 to 14 m/s at the outlet of the shield gas injection nozzle, the proposed overlay welding apparatus recesses the surface of the molten pool and can thereby irradiate at a position closer to the base material. As a result, since welding penetration depth is increased, the proposed overlay welding apparatus can suppress occurrence of a fusion defect and a weld crack without increasing the amount of heat input.
In the overlay welding method described above, if the distance between the outlet of the shield gas injection nozzle and the molten pool is increased, the flow rate of the shielding gas is reduced, and the effect of increasing the welding penetration depth is therefore reduced. Accordingly, in the overlay welding method described above, it is required that the laser welding work is performed in a state where the shield gas injection nozzle is arranged close to the molten pool. In the state where the shield gas injection nozzle is arranged close to the molten pool, it is necessarily required that a welding wire supply nozzle which supplies a welding wire to the target is arranged close to the molten pool.
The laser light which is irradiated from the shield gas injection nozzle onto a target such as the base material is reflected by the target, and then returned to a portion of the shield gas injection nozzle and/or the welding wire supply nozzle. If the shield gas injection nozzle is arranged close to the molten pool, the influence of the reflected light on the shield gas injection nozzle and welding wire supply nozzle become large. Accordingly, there arises an event that the welding head (including the shield gas injection nozzle and the welding wire supply nozzle) is damaged by melting, deformation, deficiency or the like, and the damage should be therefore prevented.
The embodiments according to the present invention was made in consideration of the circumstances mentioned above and an object thereof is an object to provide a laser welding head capable of reducing the influence of the reflected light.
In consideration of the circumstances described above, a laser welding head in accordance with the embodiments according to the present invention includes: a shield gas injection nozzle that irradiates laser light onto a target and supplies a shielding gas to the target; and a welding wire supply nozzle that supplies a welding wire to the target, wherein the shield gas injection nozzle and the welding wire supply nozzle include a main body section and a surface layer section that covers the main body section, and at least part of the surface layer section is formed by at least one of ultra-hard alloy, cermet, ceramics and MCrAlY alloy.